In a situation where your system isn’t POSTing clearing the CMOS can sometimes enable you to get back into the system for further troubleshooting.

This means you will need to replace the battery, and you can find a guide on how to do that here. The CMOS battery supplies just enough power to prevent that from happening, but it doesn’t last forever and you will eventually start to see messages saying the BIOS was reset to factory defaults.

The CMOS is necessary since the part of the motherboard that stores BIOS settings is what’s called volatile memory, meaning it loses its contents when it loses power. The battery is about the size of a quarter and is the same type that is used in wrist watches. Sometimes the only way to get back into the system is by clearing the CMOS and resetting all BIOS settings to default.ĬMOS refers to the small battery that sits on the motherboard and supplies a small amount of power to it when the system is powered down or unplugged, and is responsible for making sure the BIOS keeps the correct time and date as well as any overclock settings, among other things. When a computer fails to POST it can be for a variety of reasons, whether it’s bad hardware or a setting change in the BIOS. How do I clear the CMOS (manually reset the BIOS) on my PC?

Clear cmos msi z97 gaming 7